Today, there are numerous tests available to pregnant women that detect genetic syndromes and diseases. These screening tests are between 80-95% accurate in detecting specific disorders. The most common disorders these test screen for include Down syndrome (trisomy 21), spina bifida, and Edwards Syndrome (trisomy 18). In you are 35 years or older or have had a baby with a previous genetic disorder you are considered higher risk and the initial screening tests can be skipped.
Initial testing is screening tests only. This means that the tests will only predict an “increased risk.” If you complete the screening and your results report you are at an “increased risk,” diagnostic testing will be offered. It is important to understand that out of a 100 women that are reported to have an “increased risk” 95 of these women will have a baby without a genetic condition. In other words these tests can be false and this is important to understand. The following test are screening test.
- Non-Invasive Prenatal Testing (NIPT): This is a new test that allows examination of the fetal DNA taken from the mother’s blood. This has the potential to be very accurate without putting the fetus or mother at risk from the testing. It can be done as early as 9-10 weeks of gestation. This will not detect neural tube defects such as spina bifida.
- betaHCG: This is a hormone test that is used for confirming pregnancy, however, this blood test can also be used to indicate a risk for Down Syndrome, Trisomy 18, molar pregnancy, twins, and stillbirths. This is a part of the second trimester blood test known as the “Quad” screen.
- PAPP-A (Pregnancy Associated Plasma Protein A): This is a protein that is detected in the blood and it is decreased in conditions like Down Syndrome, Trisomy 13 and Trisomy 18. It may also predict a baby that is small for gestational age or a stillbirth. Very high levels can predict a large for gestational age baby. This may be done in the first trimester along with a nuchal translucency measurement completed by ultrasound.
- Nuchal Translucency Measurement (NT): This is a specialized ultrasound done between 11 and 14 weeks that can indicate an increased risk for Down Syndrome. This ultrasounds measures the the fluid around the baby’s neck. This is a screening that is also a part of the “Quad” screen.
- Quad Screen: This is a blood test that can be done between 15 and 22 weeks that is composed of 4 different tests. It includes maternal serum alpha-fetoprotein, maternal serum estriol, maternal beta hcg, and inhibin A. Combinations of high, low and normal levels are used to calculate a risk profile for trisomy 13, 18, 21 and neural tube defect. These risk profiles can be different depending on age, race, weight, and health history. If your gestational age of the baby are is off at all, it can significantly decrease the accuracy of the test. This test can usually be ordered and completed by your midwife.
- Materni T21: This test is a blood draw at about 10 weeks gestation and can test for trisomy 21, trisomy 18, and trisomy 13. This test has been reported to detect 99% of trisomy disorders.
- Maternal serum alpha-fetoprotein: This is the test for spina bifida and cannot be done before 15 weeks. It is part of the Quad Screen and other integrated screening, but may be done alone.
The following two tests are diagnostic tests—meaning they can diagnose your baby with certain genetic conditions. These two tests carry a risk of ending the pregnancy because they require sampling of amniotic fluid or placenta tissue. This means that there is a chance you could miscarry after the procedure.
- Chorionic Villus Sampling (CVS): This test involves removal of a small amount of the placental tissue and can be completed as early as the first trimester. This tissue sample contains fetal cells that can be tested for genetic disorders. Results are available within a week.
- Amniocentesis: This test is completed in the second trimester using a long needle to remove a small amount of fluid. The cells are then grown for about 2 weeks until the chromosomes can be closely examined for. Complications from this procedure can include cramping, bleeding, accidental rupture of the membranes, infection, and miscarriage. The risk for fetal loss is between 0.5%-1%.
Some women choose to test because they want to know before the baby is born if the baby will have a genetic disorder. This helps the woman and her partner prepare to have a child with special needs by accessing the right resources and joining support groups beforehand. In some cases women choose to terminate the pregnancy. For some women, the risks of miscarrying associated with diagnostic testing are not acceptable and the results of the test would not change their choice to keep the pregnancy so they decided not to get genetic testing done.
There is NO right answer about testing. The choice is entirely up to YOU and your partner. This information is presented as information only and not an opinion or judgment on what any pregnant woman should choose. Remember to check with your insurance company first to see what they will cover as these tests can be very pricey. Some tests may not be covered by insurance unless you are considered high risk.
I’m sure you know by now testing can be very complicated. Your midwife will arrange with you to meet with a genetic counselor to go over your personal medical history and family history if this is something you are interested in. Your midwife will also explain the test in further detail. Talk with your midwife about any questions or concerns and she can help you make an informed decision.
Resources
- http://www.acog.org/Patients/FAQs/Prenatal-Genetic-Testing-Chart-Infographic
- http://onlinelibrary.wiley.com/store/10.1111/j.1542-2011.2004.tb04230.x/asset/j.1542-2011.2004.tb04230.x.pdf;jsessionid=B7955F37EF7FAC74B5FE590A4DF0744F.f03t04?v=1&t=iz6m1fz3&s=50efbb46e8997a87d8c5a93318fd377bdde06326
- http://onlinelibrary.wiley.com/store/10.1111/jmwh.12026/asset/jmwh12026.pdf?v=1&t=iz6m2qq9&s=8b6fd1bc2e2e6913b2cf107b99651d72a5a63919
